Culture of brain tumor patient peripheral blood lymphocytes (PBL) with recombinant Interleukin-2 (rIL-2) results in the activation of lymphokine activated killer LAK cells capable of killing brain tumor cells. PBL obtained from brain tumor patients by constant flow cell separators were cultured with IL-2 for three to five days. Cells were tested for their ability to lyse fresh tumor targets. These LAK cells were infused with IL-2 into patients brain tumor cavities, via a previously placed reservoir and cell infusion system. This reservoir system was also used to draw specimens of cells and fluid to test for IL-2, evaluate surviving cell number, and LAK activities. Serial CT scans were used to assess the patients response to treatment. Brain tumor patient's PBL were cultured with IL-2 lysed tumor targets. LAK cells and IL-2 infusions were tolerated in brain tumor patients, but with toxicities, transient or permanent, related to the site of treatment. Nine patients received 15 treatments; high levels of IL-2 were found in the cyst fluid during treatment. Cell number of LAK activity decreased with time in cyst. Radiologic evidence of tumor regression was seen in one of 9 patients evaluated to date. In addition, by performing lumbar drainage with a small lumbar subarachnoid catheter, we studied the kinetics of IL-2 in the CSF, and determined the penetration of IL-2/LAK into the CSF.